Background

In addition to quality and cost, time to market is becoming an increasingly important factor in a product's success.A major contributor to product development cycles is the time needed to produce prototypes.Further, in markets where customers are demanding individually tailored components, the cost and time to produce tools or moulds can be considerable.

Rapid Prototyping (RP), also known as Solid Freeform Fabrication (SFF) processes help to overcome these problems In general the processes build complex shapes through additive processes, producing components without the use of tools.

Lamination Modelling

Laminated Object Manufacture (LOM)

Laminated Object Manufacture (LOM) cuts the component slices from thin layers of material using a CO2 laser mounted on a 2D plotter.The system most commonly uses sheets of paper stacked on top of another automatically and bonded together using an adhesive.The parts of the sheet outside the model provide support.These unwanted areas are marked with intersecting lines, which forms cubes that can be broken away from the model once complete.

Figure 1. Schematic of an LOM setup.

Advantages of LOM

The major advantages of LOM are:

•Components do not need support structures

•Only the circumference of the part is processed, whilst in most RP methods the whole part area needs to be processed

•a potential for high manufacturing speeds.

Disadvantages of LOM

The main problems are:

•Producing good bonds between layers

•Poor surface finish

•Difficulty in producing hollow parts.

Manufacture of Ceramic Components via LOM

Advanced ceramic structural components have been made with the LOM technique.0.015mm to 0.12 mm thick sheets made by tape casting have produced ceramic parts both with homogeneous and multi-layered composite microstructures.Good results have been reported with Ce-ZrO2 and Al2O3/ Ce-ZrO2 parts, which gave high strength and microstructure after sintering.

The process has been used to make Alumina, Yttria and Ceria stabilised Zirconia, Silicon Nitride, and Al2O3/ Ce-ZrO2 components with typical densities of 96% theoretical.Equipment suppliers show applications such as silicon nitride turbine blades and alumina biomedical filters, confirming that the process is best suited to applications where prototypes or small order sizes make tooling costs prohibitive.

The technique is now being used to produce mimetic bone biostructures for research purposes from alumina, zirconia and phosphate based bioceramics.Wrist, inner ear and facial bones are measured in the patient using Computer Tomography (CT) scanning.The data is processed to produce geometric models which can be exported to the LOM machine, where the components are produced.Ultimately it may be possible to produce custom bioceramic implants directly from patient specific data.